In the past, 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-6-chromanol (.alpha.-tocopherol) has been produced by condensing trimethylhydroquinone with a phytyl derivative. This condensation is generally carried out in the presence of a condensation agent such as a Lewis acid or a hydrohalic acid, (See U.S. Pat. Nos. 3,789,086; 2,723,278; and 2,411,968) at high temperatures, i.e. above 70.degree. C. In these catalytic condensation reactions, the reaction mixture is generally kept saturated with anhydrous hydrogen chloride during the reaction. The anhydrous hydrogen chloride which is generated from concentrated hydrochloric acid is pumped through the reaction mixture and recondensed.
The above process suffers from the disadvantage that it must be carried out at very high temperatures. At very high temperatures, the use of these condensing agents and hydrogen chloride provides a very corrosive mixture. Furthermore, the use of high temperatures is by itself expensive and energy consuming.
In order to avoid the use of high temperatures, it has been found that by pretreating the isophytol with amine or ammonia such as disclosed in Derwent No. 65113Y or by utilizing a mixed ether-halohydrocarbon solvent mixture such as disclosed in Derwent No. 65663Y, lower tempertures can be utilized. However, none of these processes avoid the necessity of utilizing acid catalyts and anhydrous hydrogen chloride.
In utilizing hydrogen chloride, the spent hydrogen chloride is recycled after purification. In order to do this, a considerable amount of the equipment is required solely for processing hydrogen chloride. Also, another disadvantage of this process is that the quality of the alpha-tocopherol produced presents a purification problem. The impurities in alpha-tocopherol are difficult to remove since the crude alpha-tocopherol, under the conditions of fractional distillation, starts to decompose. Therefore, in order to purify the crude alpha-tocopherol, it must be converted to a alpha-tocopheryl acetate by reaction with acetic anhydride. The acetate which is fractionally distilled is hydrolyzed back to alpha-tocopherol. Even after this extensive purification, the purity of alpha-tocopherol is only between 90-96% with major losses in yield since many of the impurities are compounds that are closely related to alpha-tocopherol. In utilizing this procedure, it has been found that many of the impurities have the same molecular weight and almost the same boiling point as alpha-tocopherol and are thus practically impossible to remove by standard purification techniques.